fix(routing): explicit mode keeps a skip_reply round private and streams where delivery routes; a resumed turn delivers in order

changelog.d/explicit-skip-reply-private.fixed.md

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+- In explicit prose routing, when a round calls `skip_reply` itself (in
+  native tool mode, and not from a `code_execution` script), the prose
+  gateway no longer delivers or bounces that round's plain text.
+  `skip_reply` promises that "Any plain text you wrote this turn stays
+  private and is NOT posted". The round's segments used to go through the
+  gateway like any other round's. Unprefixed text with no destination
+  bounced: it went onto the clipboard for an `{{unsent}}` resend, got a
+  bounce notice and could wake the resident again. Unprefixed text after a
+  destination set earlier in the turn was published there. Now none of that
+  round's envelopes is delivered or bounced, and none moves the destination
+  or asks for a continuation. A `>>skip_reply {{unsent}}` in it still sets
+  the retained text aside. A valid destination prefix, or a destination set
+  earlier in the turn, can still send the round's text through the live
+  outgoing stream as it is written.
+- Explicit prose routing no longer streams unprefixed text to the trigger
+  channel. The MCPL outgoing stream (`channels/outgoing/chunk` and
+  `complete`) started with the trigger channel as its destination, so a
+  streaming-capable server there received text that delivery would bounce.
+  It now starts with no destination on a fresh turn, since explicit text has
+  none until a `>>` prefix names one. When a tool-result-guard retry or a
+  budget restart resumes the turn, it starts at the destination the turn's
+  delivered rounds have set, decided at each round's end, so a private
+  round's prefix doesn't count. The stream also reads a `>>` prefix after
+  any leading whitespace, and ends its target at any whitespace, as delivery
+  does, rather than streaming such a line as text or dropping it. The stream
+  parses each round's text from the start of a line, as delivery parses each
+  round on its own: a round that began with a `>>` prefix streamed it as
+  text to the previous round's destination. A round's later text block
+  starts a new line, as delivery joins a round's text blocks with a newline.
+  At each round's end, and when the membrane retries a refused attempt, the
+  stream returns to the turn's destination, so a private round's prefix, a
+  `>>skip_reply` envelope or a target that didn't resolve no longer moves
+  where later rounds stream.
+- A turn resumed by a tool-result-guard retry or a budget restart now queues
+  its prose deliveries behind the turn's earlier ones, in every mode, so the
+  turn delivers in the order it wrote. Before, a resumed reply could be
+  delivered ahead of an earlier round's queued envelope, to the destination
+  that envelope was about to change. In explicit mode, a round's `>>`
+  targets are resolved once, when the round ends, and its queued delivery
+  posts to those channels.